can any one suggest the perfect measurments for building 1/35 scale ruined building with regards to doors and windows and the size of the building itself eg a country house. i would like to use plaster boards as my set up.
thanks....

Well you need to figure the measurement of the real thing, first. Doors are probably the same size (at least approx.) as today. The windows depend on the style and type of the building. You can take a reference picture and try to guess the unknown measurement based on any near standing object of a known size.

Then just scale it down to 1/35. It just means that 1mm on your model represents 35 mm in the reality. So the real 1800 mm door would be modelled as (1800 / 35 =) 51.5 mm in 1/35 scale.

I just really hope I got the math right here...

If you want "ready"ruins,check Mini-Art page in:miniart-models.com!